A mutant of Neurospora crassa, ANT-1, has been isolated that is defective in the two alternate respiratory pathways found in Neurospora mitochondria. This mutant has been used to select for mutations that affect mitochondrial energy transduction. Mutants have been isolated that are resistant to oligomycin or are defective in succinic dehydrogenase. The genetics of these mutants will be studied in detail and attempts will be made to identify its mutant gene products. Attempts will also be made to select mutants that are resistant to the drugs aurovertin, leucinostatin, paramomycin and carboxyatractyloside.